Month: May 2016

How would you describe the life cycle of a single-celled animal compared to the life cycle of a bird? Or compared to your life cycle, for that matter?

Paramecium multinucleatum, a single-celled animal

Birds, like humans, are made up of many, many cells (and about as many microbes as human cells, too!), and take years to grow large enough to find a mate and reproduce. You probably can think of a few ways a single-celled animal differs right away: many do not need a mate, but can just divide in two. It only takes a few hours to a few days for them to grow large enough to divide.

A bdelloid rotifer, about the same size as the Paramecium above, also does not need a mate even though it is multicellular.

But many single-celled animals differ in another important way. If our environment gets too cold or we cannot find enough food or water, those conditions can kill us. Many single-celled animals, however, can retreat into a hard-walled structure, forming a cyst that can survive a long time without eating, and even survive freezing or drying out. This is one strategy that seeming super-organisms might use to live on Antarctic glaciers or in the Arizona desert, for example.

The pink animal in the top photo is in the genus Blepharisma, and is a similar size to the Paramecium. When Blepharisma are in trouble, they form the small pinkish cysts in the lower photo.

This ability to survive as cysts might be important for understanding which species are where. Such animals are in some ways more like a plant, with a seed bank in the soil waiting for rain, than like a bird. In fact, this superpower is one that other microscopic but multicellular animals, like rotifers, also possess.

The structure on the left is a cyst-like structure of the rotifer (genus Philodina) pictured above. (The one on the right is another sort of rotifer, in genus Monostyla.)

Maybe time for a new superhero in the Marvel universe? One with the power to transform into an impervious little sphere at the first sign of trouble? Cystgirl? Cystman?